Blades for wind power generation currently used is mainly made of glass fiber reinforced plastics (GFRP), and the blade itself is an insulator and has no electrical conductivity. Accordingly, in an era of a small wind power generator it was considered that the blade was not struck by lightning. However, as the wind power generator grows in size, damage of the blade stuck by the lightning is increased. Accordingly, a method of attaching a member (lightning receptor) made of metal to the blade and connecting a lead line (down conductor) to the metallic member and the ground has been generalized. Various shapes or types of the lightning receptors have been proposed and put to practical use.
For example, in PTL 1, there is disclosed a lightning protection system of wind power generation including a conductor ring provided on a blade, and a non-linear resistance body or a zinc oxide type lightning element provided in a rotor case which is equipped with a wind power generator therein, in which the non-linear resistance body or the zinc oxide type lightning element faces the conductor ring.
In PTL 2, there is disclosed a lightning protection structure capable of improving a lightning protection effect by installing an early streamer launching type lightning conductor above the apparatus, in addition to the wind turbine blades which are electrically insulated.
Also, in order to prevent the blade made from the GFRP, in PTL 3, there is disclosed a lightning arrester equipment for a wind turbine capable of eliminating a blade from stroke of lightning, in which one or plural electrode plates are attached between tips and roots of blades to make lightning current flow from an electrode plate to an electrode plate or creep-discharge directly on a blade surface from the electrode plate. Lightning current collected in a hub is led to the ground from the hub through a nacelle and a tower, so that burn of the blade can be completely prevented.
In PTL 4, there is disclosed an arrestor for a wind turbine power generator, in which a metal member opposed to a lower end of a blade at a position apart therefrom is attached to a wind turbine tower, and the metal member is positioned in the vicinity of a tip of a blade largely rotating around the metal member, so that charges on the blade are discharged to the metal member which approaches thereto for every rotation of the blade so as to prevent lightning from striking the blade.
In PTL 5, there is disclosed a thunder resistant protecting device, wherein a mounting base for a protruded lightning rod of a heat-resistant conductive material is fitted to the tip of a blade of a wind turbine which drives a generator so as to cover the tip, then the protruded lightning rod, which absorbs light/thermal energy generated by the thunderbolt and is thermally fused, is detachably mounted to the mounting base for the protruded lightning rod. The protruded lightning rod is projected in a parabolic form from an outer surface of the mounting base for the protruded lightning rod, the mounting base for the protruded lightning rod and a conductive hub at a central portion of the blade are electrically connected by a lightning protection conductor arranged in the blade, a discharge bulb body which is thermally fused is detachably mounted to the end face at the generator side of the hub, a conductive discharge ring which is confronted with a discharge bulb body through a discharge gap is fitted to the end at the wind turbine side of a nacelle, and then the discharge ring is grounded through a lightning protection lead wire.